Like many I am hooked by the blue glow and the shapely bottles. That aside, I'm very curious if the KT66 brings more output. I'll be on the fringe of acceptability with the stock 25 watts. If different tubes can urge even a couple of watts more out of the amp that would weigh stongly in me considering them. I'll be running with the stock EL34s for sure right out of the gate.

We're doing one now and it looks like the bill is going to be around $700 not including tubes. That will turn a MK III into a MK IV with cryo treated beeswax caps.

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What about the Hazen modification? I don't think it would work with a KT66.

The Hazen Grid Mod will have no effect on this tube.

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With upgrading the to the KT66 tube, I am assuming that you lose the Hazen grid mod? How would you compare the sound of the EL34 vs. the KT66 in the new Torii?

The Hazen Grid Mod takes advantage of the internal construction of the EL34 to make it a better sounding tube, and it does. With the circuit changes in the new MK IV, the KT66 is a better fit resulting in an even better sound. The presentation is far better balanced and you get the full range of the volume control without any clipping. Due to the increased voltage swing we introduced into the phase inverter and input stage, EL34's have more gain than they did in the MK III. The result is an amp that is at full power with the volume control barely hitting the half way mark... it can be a little aggressive.

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Does anyone know if the wait time to upgrade our MKIII is the same as buying the new model? I am tempted to sell my MKIII and use those funds toward the MKIV but the thought of being without an amp for months is scary! I guess that will also depend on the cost to upgrade.

Upgrades are typically a two week turnaround, however, if everyone with a MK III sent them in right away, the wait could certainly grow.

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Can the Torii MK.4 use EL34 "Or" KT66's interchangeably?

Yes, it can ship with either one. The TORII MK IV has a new toggle switch that allows you to adjust the bass to perfection with either tube.

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This is what I understand to be the case. Two amps for one! From Steve's post with pic: "These hand picked Tungsol KT66's are a $100 upgrade over the stock EL34's."

This is absolutely correct, the MKIV is a completely different amplifier with either set of tubes and it would be like owning two different amps.

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Like many I am hooked by the blue glow and the shapely bottles. That aside, I'm very curious if the KT66 brings more output. I'll be on the fringe of acceptability with the stock 25 watts. If different tubes can urge even a couple of watts more out of the amp that would weigh stongly in me considering them. I'll be running with the stock EL34s for sure right out of the gate.

The KT66 brings a few more watts to the table, yes. It also has less gain, meaning you have to turn the volume control to a higher position to reach the same loudness as you do with EL34.

The white knobs are the redone treble control. The effect of this control is so subtle now, that MKIII owners will think it doesn't even work. It makes a small adjustment from about 8 kHz on up.

The silver toggle switch next to it is the new reconstructive feedback switch. Probably the coolest feature on the whole amp. Reduces the phase angle and dramatically improves presence. It's on a switch because it's success or failure is based on the speaker load. Show it the wrong load (especially with EL34's) and it will squeal like a stuck pig (osculate) For example, plugging a pair of headphones into the speaker jacks instead of speakers with this switch on would cause the osculation. Turning the switch off would stop the osculation.

The switch directly centered behind the binding posts is the impedance switch for the speakers. Same as always, can be configured to 4 and 8 ohm or 8 and 16 ohm speakers.

The toggle switches to the left and right of the volume control are the bass switches the control how tight the bass is on a given set of speakers with either set of output tubes. On the MK III amps there will only be one switch that does both channels at the same time instead of two as shown here.

The center toggle switch between the small OC2 tubes is now the input switch allowing you to select between the two sources.

Due to the increased voltage swing we introduced into the phase inverter and input stage, EL34's have more gain than they did in the MK III. The result is an amp that is at full power with the volume control barely hitting the half way mark... it can be a little aggressive.

Does this imply that the EL34s are being run hard with more heat? Also, does this mean that running without a preamp would make volume adjustments a little more touchy?

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The KT66 brings a few more watts to the table, yes. It also has less gain, meaning you have to turn the volume control to a higher position to reach the same loudness as you do with EL34.

Care to estimate how many more watts? Which tube works harder in this amp? Are there any implications to one lasting longer than the other due to the way it operates?

Neither tube is being run hard in the amp. The EL34 is an easier tube to drive, that is why it develops more gain than the KT66. The added gain of the EL34 would make using a preamp touchier than it was on a MK III, meaning smaller adjustments to the volume control to effect the same changes to level as before.

Welcome back. Steve said earlier to order a MkIII and then MkIV build will be automatic and specifics can be sorted out later, with plenty of leed time before build time. The Jupiter caps are standard, and we know the KT66 upgrade is 100.

I would just put what you want in the message box of the order form and ask Sarah to let you know pricing details for the extra volume control as they become available along with the approximate build date so you can be sure all is well when it comes up.

This is what I would do anyway if you want to get a place in line locked in. Or call.

I had an interesting evening with the TORII MK IV last night. I played it on my corner horns, which for that amplifier are a worse case scenario when it comes to bass at high volumes. Since the amp likes to put out more current into higher impedances, horns of this design can get a touch boomy.

This very tendency of the amplifier to sound boomy on the corner horns makes the other 12 pair of speakers in our listening room sound better than they actually are… but nevertheless, it is the worse case scenario you have to design for, so on we marched for the next four hours with the MK IV on the corner horns.

The new MK IV bass switch really alleviates this tendency with these speakers, so it was of course on the entire time. And after shifting to more demeaning material, the positive feedback switch was turned off, dropping the dynamics slightly and allowing me to crank the amp a bit harder. Then during the acid test, I used electronic music which has wall cracking low bass at high SPL due to massive compression, I even switched speaker taps with the speaker impedance switch to the softer setting. These three adjustments kept things tight and clean as the evening matured and the material continued to get more and more challenging.

It is interesting to note, that after four hours I gave up on the EL34's and installed the KT66's that I designed the MK IV to favor. The TORII's tendency to get a little over the top on these speakers had now disappeared and the amplifier became as linear as if there were feedback applied. The midrange and top end and bottom end are virtually perfect now, and at any volume. Nothing changes from modest volumes to louder playback levels and there is a very apparent increase in overall headroom and power.

Naturally, this was a real thrill as I was well into hour five and playing my challenging tracks to see how well the amplifier maintains it's usable power. Suddenly this simple tube change made everything twice as good, and I realized I didn't need the speaker impedance switch on the softer setting anymore… so I switched it back and everything got 3dB louder, even fuller, much deeper, and without a trace of strain. It was truly a wow moment…

Things are getting really fun now… so sucked into the recordings with this latest bust of flavor, another hour went by and I realized I didn't need the bass tighten switch on, so I turned it off. Everything was still fine, nice and tight, but now suddenly even deeper. Again not a hint of strain. It was wow moment no. 2, and I have to say that things are getting amazingly loud without sounding bad… quite the opposite in fact. (this is btw the epitome of usable power).

Another half hour went by and I realized I hadn't turned on the positive feedback switches yet. So, without further ado, I just turned them on. This was more like a holy-crap movement where I just stood there in the sweet spot of my horns in disbelief at the presence… not to mention the room shifting dynamics that simply felt real.

Ratcheting the performance and sound up three times like that I'd have to equate the experience to a drag race, where you come out of the gate with a nice wheel stand, wind it out and then hit second gear followed by a nice long pull and then hit third gear. You get a little sideways for a moment with the meat on your face pulling back toward your ears from the aggressive pull until everything is a blur… and you then float into your out of body experience. So, clearly the TORII MK IV is a competent space ship like it's predecessors all were, but this one has gears!